| Cover Page Document | Sep. 30, 2020 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Document Period End Date | Sep. 30, 2020 |
| Entity Registrant Name | Allegiant Travel Company |
| Entity Incorporation, State or Country Code | NV |
| Entity File Number | 001-33166 |
| Entity Tax Identification Number | 20-4745737 |
| Entity Address, Address Line One | 1201 North Town Center Drive |
| Entity Address, City or Town | Las Vegas, |
| Entity Address, State or Province | NV |
| Entity Address, Postal Zip Code | 89144 |
| City Area Code | 702 |
| Local Phone Number | 851-7300 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Entity Emerging Growth Company | false |
| Entity Central Index Key | 0001362468 |
| Amendment Flag | false |
